VARIATIONAL ANALYSIS OF SINGLE-MODE GRADED-INDEX FIBERS BASED ON A NOVEL APPROXIMATION OF THE FUNDAMENTAL MODAL FIELD

A novel and extremely accurate near Gaussian approximation for the fun damental mode in single-mode fibers having arbitrary index profiles is proposed and verified by the variational method. The spot size calcul ated from our approximation matches closely the analytical and exact n umerical results for step and parabolic index fibers over a large rang e of values of the normalized frequency V. For the low V region where the Gaussian approximation is not accurate, our results are suitable t o accurately predict the propagation characteristics of devices such a s directional couplers involving evanescent field coupling. (C) 1996 S ociety of Photo-Optical instrumentation Engineers.